1. Field of the Invention
This invention relates to a method for the production of spinel single crystal filaments which are excellent in heat-resistance, anti-corrosion, mechanical strength, etc. and are useful as high-temperature heat insulators and fiber-reinforcing filaments. More particularly, this invention relates to a method which enables spinel single crystal filaments measuring not more than several .mu.m in diameter and suitable for a wide variety of applications to be produced expeditiously with high productivity in a large quantity in one operation.
2. Prior Art Statement
The manufacture of a ceramic material into filaments can be attained by such methods as the sol-gel method. The filaments which are produced by these methods are polycrystals and, therefore, are liable to be deteriorated by the growth of grains at elevated temperatures. They are moreover inferior to single crystal filaments in such properties as mechanical strength. Numerous methods for producing single crystal filaments of ceramic materials have therefore been developed to date.
As regards spinel (MgAl.sub.2 O.sub.4), it is a known practice to produce single crystal filaments of this ceramic material by the laser heat floating zone method (J. Sigalovsky et al.,: J. Crystal Growth Vol. 134, p 313, 1993). This method, developed by scaling down the floating zone method normally used for growing single crystals measuring several mm in diameter, is adapted for growth of extremely thin single crystals from extremely thin raw material rods.
The laser heat floating zone method is deficient in productivity, however, and is capable of producing only one filament per operation. Further, this method cannot easily produce thin filaments measuring less than some tens of .mu.m in diameter. The filaments therefore have practical utility only in limited applications.